The present invention relates generally to a method and apparatus for screening a patient to detect diseases and abnormalities of the eyes and lids.
More particularly, this invention relates to a method and apparatus for photoscreening a patient by generating wavelength-encoded images of a patient""s eyes and analyzing these images to detect diseases and other abnormalities.
It is well known that approximately 2-5% of children will develop some degree of amblyopia and another 15%-20% possess some form of visual malady. Screening eyes to detect diseases and abnormalities, such as refractive errors, both spherical and cylindrical in optical power, ocular alignment, media opacities, and ptosis, is very important because if these diseases are not corrected before the ages of 7 to 9, a person may suffer irreversible vision loss. Screening eyes in young children accurately and consistently, however, is not an easy task, especially when computer automated diagnosis in involved.
As mentioned previously, many of these diseases and abnormalities must be detected and corrected at an early age, and, accordingly, the typical screening patient is a child in preschool through third grade. Generally, patients in this age group have a very short attention span, which makes it difficult to perform an accurate screening of the eye. As a result, screening tests for patients in this age group must be expeditious, simple, passive (i.e., no patient-technician interaction), non-intrusive, and portable enough for field-testing in the school environment. One type of screening test that satisfies these criteria is photoscreening.
Photoscreening is the process of taking a photograph of the patient""s eyes and analyzing that photograph to detect diseases and other abnormalities. In general photoscreening systems include a camera (film or digital), and single, multiple, or ring-type flashes located near (or on) the camera""s optical axis. By simultaneously illuminating the eyes with the flash and taking a photograph, one creates an image that may be analyzed to detect diseases and other abnormalities in the eyes.
It is known in the art that Caucasians produce a distinctive red retinal reflex, or retinal return reflection in a photoscreened image. This red retinal reflection is visible to the camera when illuminated by a near (or on) axis flash and the pupils are sufficiently dilated. Other ethnic groups, however, differ rather dramatically. Persons from African-American, Asian, and Hispanic descent do not, in general, produce a red retinal reflex and, in fact, with an eye that can focus properly, off axis photoscreening may produce no detectable retinal reflex. This is particularly alarming since it may be difficult, if not impossible, to detect cataracts or other media opacities in these ethnic groups via traditional photoscreening techniques. The present invention overcomes the deficiencies associated with traditional photoscreening and allows a robust method for computer-aided screening.
For example, U.S. Pat. No. 5,989,194 issued to Davenport et al. on Nov. 23, 1999 and entitled, xe2x80x9cMethod and Apparatus for Detecting Ocular Disease and Abnormalitiesxe2x80x9d and U.S. Pat. No. 6,095,989 issued to Hay et al. on Aug. 1, 2000 and entitled, xe2x80x9cOptical recognition methods for locating eyesxe2x80x9d (continuation-in-part of U.S. Pat. Nos. 5,632,282 and 5,355,895.) both teach a screening system which includes a singular flash and provides information in only one meridian of the eye. As a result, these systems are unable to detect astigmatism in some axes of the eye and, in addition, neither of these patents allows one to obtain quantitative numbers relating to the patient""s pupil size or baseline retinal reflectivity prior to the actual photoscreening process. It should also be noted that the Hay patent includes extensive techniques for computer analysis of typical photoscreened images and, therefore, has inherent difficulties analyzing these images on the minority groups mentioned earlier. The contention is that robust analysis of traditional (single, double, or ring type off-axis flash systems) photoscreened images for media opacities and refractive errors is difficult to perform, and is especially difficult to analyze via computer image processing. The present invention, with its novel infrared prescreening capabilities and wavelength encoded image acquisition, allows for robust image analyses across all ethnic groups by both manual and digital means.
A two-flash screening system is described in U.S. Pat. No. 4,523,820 issued to Kaakinen on Jun. 18, 1985, and entitled xe2x80x9cProcedure and Means for Establishing and Recording Errors of the Eyexe2x80x9d. The ""820 patent teaches a system and method for obtaining a photograph of a patient""s eyes by simultaneously triggering two flashes located in different meridians of the eye. It is true that this system is more robust in the detection of astigmatism over single flash systems, but, because both flashes are triggered simultaneously and overlap in the resulting photograph, it is difficult to interpret the contributions made from each flash. While it may be possible to determine that a patient""s vision has sphere and cylinder errors, the overlapped images make it difficult to specify the extent of these errors. This system also suffers from problems associated with traditional photoscreening systems mentioned earlier.
Additional two-flash photoscreening systems are described in U.S. Pat. No. 4,989,968 issued to Friedman on Feb. 5, 1991 and entitled, xe2x80x9cPhotocreening Camera Systemxe2x80x9d and U.S. Pat. No. 6,089,715 issued to Hoover et al. on Jul. 18, 2000 and entitled xe2x80x9cAutomated Photo refractive Screeningxe2x80x9d. Both of these patents describe systems that are similar to the ones in the ""820 patent, except that the flashes are either mechanically rotated or the camera is physically rotated in order to get two singular photographs, each containing information regarding different meridians of the eye. The primary problem with both of these systems is the 15 to 20 second time delay between the flashes. During this time delay, the patient""s pupils may change in diameter, the eyes may change in accommodation, or the eyes may align differently, any of which will cause a significant increase in false positive screenings. Again, both of these systems suffer from problems associated with traditional photoscreening systems mentioned earlier. It should be noted that the algorithms employed by the Hoover patent base their pupil detection on the red retinal reflex (step 52 ""715 patent) in order to perform computer-aided diagnosis.
Finally, a screening system utilizing a ring flash is disclosed in U.S. Pat. No. 4,586,796 issued to Molteno on May 6, 1986 and entitled, xe2x80x9cTesting to Determine the Fixation and Focusing of Living Eyesxe2x80x9d. While this system does allow one to determine that there is a problem with the eyes, determining the type of problem is difficult. This is true because the ring flash is symmetrical around the optical axis and, as a result, while it is possible to detect both cylindrical and spherical optical errors, it is unclear in the photograph whether the spherical error is myopic or hyperopic in nature or in which axis the cylinder power is oriented.
Thus, what is needed is a robust system and method for screening eyes that allows one to detect and identify various types of diseases and abnormalities in the eyes with a high degree of accuracy and specificity across all ethnic groups.
The present invention provides an apparatus and method for generating 1.) infrared illuminated images, and 2.) wavelength-encoded images (i.e., the images are generated using different wavelengths of light) of a patient""s eyes and 3.) analyzing these images to detect diseases and abnormalities.
The apparatus includes a device for recording images of a patient""s eyes while 1.) the eyes are being illuminated with infrared light, and 2.) the eyes are being simultaneously illuminated with wavelength-encoded light in at least two different meridians of the eyes. The apparatus also includes a light source for 1.) illuminating the patient""s eyes with infrared light, and 2.) for illuminating the patient""s eyes with wavelength encoded light. Finally, the apparatus includes a system for controlling both the image-recording device and the wavelength encoded light sources.
The method includes the steps of illuminating and recording images of the patient""s eyes with infrared light. These infrared images are used to determine the pupil size, baseline retinal reflectivity, and to identify non-refractive errors, such as cataracts, esotropia, and exotropia. These steps are immediately followed by the simultaneous triggering of multiple, wavelength encoded light sources, in at least two different meridians of the patient""s eyes. These wavelength-encoded images are used to identify refractive errors, such as astigmatism, myopia, and hyperopia. In addition, by capturing the images simultaneously, the present invention eliminates errors caused by changes in dilation, accommodation, or alignment. Furthermore, the decoding step eliminates the overlapping information problem created by the ""820 patent by separating the wavelength-encoded image into two wavelength-decoded images, each containing an image of the patient""s eyes generated by a different color of light.
In one embodiment, the image-recording device includes a high-speed digital camera, the infrared light source includes a plurality of infrared light-emitting diodes (LEDs), the wavelength encoded light sources include a pair of commercially available off-the-shelf flashes commonly used with cameras, and the control system includes a computer system. The high-speed digital camera, which normally includes an infrared filter, is made sensitive to infrared light by removing the filter. This allows the camera to record both visible and infrared images. Each of the flashes includes two filters, one encoded and operable to pass only one color of light (red or green), and a second encoded to block infrared light. The infrared filter is used so each flash will emit only one color and facilitate subsequent decoding. In an alternative embodiment, the light source includes a ring flash with one wavelength encoded filter covering one meridian of the ring flash, a second wavelength encoded filter covering a second meridian of the ring flash, and the remainder of the ring flash covered by a filter that blocks all light generated by the remainder of the ring flash. In both embodiments the computer system controls the camera and the flashes (or flash in the case of the ring flash). In addition, the computer system decodes the wavelength-encoded image of the patient""s eyes into wavelength-decoded images and analyzes the infrared and decoded images to determine pupil size, non-refractive errors, and refractive errors.